Many different types of toilet flush valve and overflow pipe assemblies have been provided in the prior art. Some of them have included ball valves, but the valves have not been of such form as to provide sufficient flexibility for effective sealing on their cooperating seats as well as sufficient buoyancy to act as floats in aiding in unseating and movement to opened position. One type of prior art flush valves has also included a single small water container which is intended to act as a counterbalance when the valve is opened and to provide a time-delay as it slowly drains and eventually permits the valve to close. However, the usual container of this type is mounted so as to produce an imbalance in the assembly which interferes with the pivoting of the valve support and, moreover usually interferes with the overflow pipe and occupies too much of the limited space.